Platinum-Iridium alloy A platinum alloy consisting of platinum as a base and iridium added to it. In the early years, it was believed that the solution was completely solid within the range of all components, and it was confirmed that the high temperature region was a continuous solid solution. Spinodal decomposition occurred below 975℃ :α1=α2+α3, forming an amplitude modulated structure, which expanded to 7%~99%(atomic fraction) iridium wide region at 700℃.
Natural platinum-iridium alloys are often associated with platinum ore and exist in granular form. In 1838, A.Gaudin synthesized PtiR1O alloy pellets for the first time. Iridium was initially considered a harmful element. Extensive research conducted in the mid-to-late 19th century dispelled this misconception. In 1874, PtiR1O alloy ingots weighing 250kg with uniform composition were cast in Paris as the standard material for the manufacture of international meters and kilogram weights. The prototype weights underwent ultra-high pressure tests before being accepted by the International Commission of Metroids. The density values of 11 standard kilogram weights ranged from 21.548 to 21.552g/cm. The standard resistance of platinum-iridium alloy has withstood 67 years of careful examination, and its resistance value has little change.
(1) Platinum-iridium alloys have high melting point, high density, high hardness, high strength, and high elasticity. These properties increase with the increase of iridium concentration.
(2) The alloy containing more than 10% iridium has age hardening effect and increases with the increase of iridium concentration, but the precipitation rate is low.
(3) The resistivity of Pt-Ir alloy increases with the increase of Ir concentration, while the resistance temperature coefficient decreases. Pt - iridium alloy has low contact resistance, but it is easy to be polluted by organic atmosphere, which increases the contact resistance. Platinum-iridium alloys exhibit positive thermoelectric potentials for platinum and increase with increasing iridium concentration.
(4) The addition of iridium to platinum significantly improves the chemical corrosion resistance of platinum, and alloys containing more than 30% iridium are actually not corroded by boiling aqua regal.
(5) With the increase of iridium concentration and heating temperature, the volatilization weight loss of platinum-iridium alloy increases.
(6) Platinum-iridium alloy has high deformation resistance and work hardening rate, and the work performance decreases with the increase of iridium content. The intragrystal segregation and dendrite are well developed, and the alloy can only be cold processed after high temperature hot working.
